Historic Transit of Venus Sketched by British Explorer

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Nearly 250 years ago, when the planet Venus made a rare pass
between Earth and the sun, James Cook, the intrepid British
explorer, sketched the celestial scene from the island of Tahiti
in the South Pacific. Now, skywatchers around the world have the
chance to witness the same historic event today (June 5), as
Venus again wanders across the face of our nearest star.

During his first voyage around the world, Cook drew the various
stages of the
transit of Venus as it appeared from Tahiti on June 3, 1769.
The explorer was joined by astronomer Charles Green on the
expedition, and the crew of the HMS Endeavour observed the
transit using special equipment from a spot that later took the
name "Point Venus," according to NASA officials.

Witnessing the Venus transit was one of the primary purposes of
the journey, since the celestial encounter would help astronomers
piece together key clues about the size of the solar system, NASA
officials explained. The crew made a variety of measurements
during the event, and both Cook and Green sketched what they saw.

The drawings were originally published in 1771 as part of
"Observations Made, by Appointment of the Royal Society, at King
George's Island in the South Sea; By Mr. Charles Green, Formerly
Assistant at the Royal Observatory at Greenwich, and Lieut. James
Cook, of His Majesty's Ship the Endeavour," in the journal
Philosophical Transactions.

Transits of Venus are some of the rarest planetary alignments and
skywatching sights, because they only occur in pairs eight years
apart, once every 100 years or so. In fact, Venus has only
crossed in front of the sun seven times since the invention of
the telescope. [ Venus
Transit of 2004: 51 Amazing Photos ]

Today's transit is paired with a previous one that happened on
June 8, 2004. After today, however, the next pair of Venus
transits will not occur again until the years 2117 and 2125.

As
Venus crosses the solar disk, it will appear as a small,
black blemish on the face of the sun. The transit will begin when
Venus first touches the outer edge of the sun, at around 6:03
p.m. EDT (3:03 p.m. PDT; 2203 GMT). The entire event will last
roughly seven hours.

Much of the world will be able to see the transit of Venus, and
at least one group of scientists are mimicking the historic
18th-century expeditions by watching the event unfold from
different reaches of the planet.

Members of the
Venus Twilight Experiment are equipped with solar telescopes
in Arizona, Australia, California, Hawaii, India, Japan,
Kazakhstan, the Arctic and the South Pacific to watch as Venus
crosses the sun.

Several satellites in orbit will also be monitoring the event and
collecting data on the sun and the atmosphere of Venus.

NASA astronaut Don Pettit, who is currently living and working
aboard the International Space Station, is aiming to be the first
person to
photograph the Venus transit from space. Pettit, who is
partway through a months-long stay at the orbiting outpost, will
take pictures of the scene from the station's seven-windowed
Cupola observatory.

WARNING: If you plan to observe the transit of
Venus in person, it is very important to exercise caution and
protect your eyes. It is very dangerous to stare directly
at the sun. Special eclipse glasses or solar filters for
telescopes are needed to avoid permanently damaging your eyes.

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